Electronic fuel control systems are used in internal combustion engines to precisely meter the amount of fuel required for varying engine requirements. Such systems vary the amount of fuel delivered for combustion in response to multiple system inputs, including the concentration of oxygen in the exhaust gas produced by combustion of air and fuel. Typical electronic fuel control systems operate in closed-loop mode responsive to sensed exhaust gas oxygen levels in order to maintain the ratio of air and fuel at or near stoichiometry for purposes of reducing undesirable exhaust emissions, particularly in connection with a catalytic converter.
Conventional fuel control systems, however, are designed for use in vehicles powered by liquid fuels such as gasoline, ethanol, methanol, or mixtures thereof. Such systems are not readily adaptable for use in vehicles powered by non-conventional fuels, such as liquid propane gas (LPG), or compressed natural gas.
Liquid propane gas powered vehicles are desirable, however, because of their reduced fuel costs. Presently, LPG is available for approximately one-third the cost of gasoline.
Although LPG powered vehicles cost less to operate than conventional fueled vehicles, presently available LPG engine control systems are prone to back-firing. To reduce sensitivity to back-firing, the air/fuel mixture of existing systems must be adjusted on the rich side of stoichiometry. As a result, fuel economy and engine performance suffer, and emission levels increase.